rear end questions

[Malfunkzhun]

I am currently working on a 1963 GMC to handle around 450 hp. i have a 10 Bolt Dana 44 posi. gear ratio is about 3.56 and has 30 spline axels..
I also have a 1977 12 bolt with a gear ratio of about 4.10 and also 30 spline axels sittin in yard.. which would be better to use or able to handle better if i were to do a few burnouts or take to the track??

[Rich 5150 69]

Either one will hold, the problem will come when you start changing suspension and put on sticky tires, wnen it hooks you`ll find out the strength..

[Malfunkzhun]

Ok thanks.. such a big help

[ozzyman]

3.56 would be a better axle for daily driver, 4.10s would be good for the track, since you have both I would build the 4.10 for the track. A swap wouldn't be too difficult for a fun day at the track

[Captainfab]

Personally, I would go with the 12 bolt. It will bolt right up to your leaf springs. The 12 bolt should have bigger brakes, plus it is all around a little stouter than a Dana 44. Have you verified that the 12 bolt has 4.10's or are you just guessing? I would pull the cover and have a look.

[mud.man.rj]

My 12 bolt blew a spider side gear tooth right thru the rear cover last night. It is a 73 and up Gov. lock, stay away from that style. I was trying to figure out if an Auburn or Eaton posi will be a direct swap into the same 12 bolt housing. here are a few pic's. To much tire and 500 plus ponies.




So anyone know about the swap choices.

[Malfunkzhun]

I counted 41 teeth on rear axle ring, but thats it.. so i was guessing its 4.10.. 12 bolt is actually 2 inches wider then 10 bolt.. so might have to do some modification.

[mud.man.rj]

You have to count the pinion too then divide the 41 x pinion, like 41divided by 11 = 3.73 ratio. The big ring gear always is marked (stamped) with both ratios, so find it and divided one by the other, then you know for sure.

[Malfunkzhun]

Yes.. just took apart.. it is 3.73.. the only thing i notice it tthat like i said, 12 bolt is 2 inches wider, but i guess that shouldn't be too much of a problem to modify.

[Captainfab]

Yes the late '70 to '82 12 bolts are 1-1/2" wider than the early '70 and earlier 12 bolts, as well as the Dana 44's. You'll just have to choose your wheel backspacing accordingly. I know many guys run the '71-'87 rear ends under these trucks, so it can be done. Narrowing the rear end can be done, but it does cost a little to be done correctly.

Originally Posted by Malfunkzhun

Yes.. just took apart.. it is 3.73.. the only thing i notice it tthat like i said, 12 bolt is 2 inches wider, but i guess that shouldn't be too much of a problem to modify.

[Captainfab]

Any posi or locker made for a truck 12 bolt will fit into a truck 12 bolt housing from '63 thru '82.

With that much power and those big tires you will likely have other issues with that 12 bolt unless you spend some money on it. You will also want to weld the axle tubes to the center section.

Originally Posted by mud.man.rj

My 12 bolt blew a spider side gear tooth right thru the rear cover last night. It is a 73 and up Gov. lock, stay away from that style. I was trying to figure out if an Auburn or Eaton posi will be a direct swap into the same 12 bolt housing. here are a few pic's. To much tire and 500 plus ponies.
So anyone know about the swap choices.